In the production of rigid boards, slabs, billets, logs, or the like, a foamable thermoplastic resin such as styrene or polyurethane incorporating a blowing agent is extruded through a die orifice. As soon as the extrudate leaves the die orifice, it is at a much lower pressure, preferably a vacuum, and immediately begins to expand and move away from the die orifice. The extrudate will expand away from the die orifice increasing in size three-dimensionally. If such expansion is not properly controlled and the extrudate properly directed from the die orifice, particularly as the extrudate cools and begins to cure or set, undesirable dimensional variations may result such as corrugations as well as undesirable variations in density and cell orientation. It is important that the product be of uniform density, uniform thickness and with minimum cell distortion. It also is important that the finished surface be free of distortions, surface blemishes, cracks or the like.
Various apparatus and methods of forming low density boards, slabs, billets, logs, or the like are known, and examples thereof may be seen in U.S. Pat. Nos. 3,704,083; 4,044,084; 4,211,739 and 4,234,529. Generally, the foamable material is extruded into a vacuum chamber and its expansion therein may be properly controlled by various forming, shaping and finishing apparatus to obtain the desired product. As disclosed in U.S. Pat. No. 4,234,529, a forming roll assembly is positioned adjacent and immediately downstream of the die orifice of the extrusion die which preferably is arcuate. The forming roll assembly includes opposed sets of curved rolls extending generally circularly of the center of the extrusion die on opposite sides of the extrudate pass line or flow path. The rolls on at least one side of the extrudate pass line are air balanced or floated so that the pressure on the opposite side of the balance essentially represents a true approximation of the pressure of the roll directly against the extrudate. After passing between the roll sets, the extrudate passes through a surface finishing apparatus which comprises relatively large area top and bottom plates or belts backed by such plates. One or both of such plates or belts may be floatingly supported in the same manner as each of the rolls of the roll sets as aforedescribed, and one is pivotally supported at its center of gravity in order to permit it to pivot with respect to the extrudate pass line.
The forming, shaping and finishing apparatus disclosed in such U.S. Pat. No. 4,234,529, while useful in forming billets, logs, and the like, is more suited to forming boards and slabs which are considerably more wide than thick. Such boards and slabs are useful as insulation and sheathing in houses and buildings. Applicants herein have devised a foam extrusion apparatus which is suited particularly to the formation of billets, logs, or the like which have a substantial thickness in relation to their width. Such billets and logs are useful as flotation in watercraft and/or as stock from which various articles may be formed such as ornaments and packing material.
In addition to the apparatus and methods disclosed in the aforementioned patents, various other apparatus and methods are known in the art and examples thereof may be seen in U.S. Pat. Nos. 2,740,157; 3,431,163; 3,897,528, and 3,914,085, and in U.S. Pat. No. Re. 27,243. In the first of these patents, there is described an apparatus which includes generally parallel foam shaping members positioned on opposite sides of the extrudate pass line immediately downstream from the die orifice. In one embodiment, each shaping member includes two diverging rows of rolls which are supported between parallel frame plates. Provision is made for slight adjustment of such frame plates to vary slightly the spacing and relative angular inclination of the two diverging rows of rolls. In another embodiment disclosed in such patent, the shaping members are in the form of two substantially parallel plates, one of which has a hinged extension downstream of the die orifice which is spring biased at its distal end towards a fixed downstream extension of the other shaping member.
In U.S. Pat. No. 3,431,163, the extrusion apparatus described includes opposed steel plates having planar surfaces which define a zone into which the foamable material is extruded. Such steel plates are set at various angles to each other as desired.
In U.S. Pat. No. 3,897,528, the extrusion apparatus described also comprises opposed shaping members. Such shaping members each include a fixed plate rigidly affixed to the extrusion die and a hinged plate pivotally affixed to the fixed plate downstream of the die orifice. The hinged plate of each shaping member is capable of limited angular adjustment relative to the fixed plate, such adjustment being effected by positioning means such as a hydraulic cylinder.
In U.S. Pat. No.3,914,085, an extrudate sizing or guide assembly is affixed to the face of the extrusion die. Affixed to such assembly and remotely from the die face are opposed forming members. The forming members are pivotally attached to such assembly and positioned by positioning means such as screws or hydraulic cylinders. A somewhat similar arrangement is disclosed in Canadian Pat. No. 451,864.
In U.S. Pat. No. Re. 27,243, a puller component is located downstream of an extrusion die. The puller component consists of two parallel endless belt assemblies, one of which is adjustable towards and away from the other. Both endless belts are driven by an electric motor through an endless chain.